Apparatus for electrolytic oxidation or reduction, concentration, and separation of elements in solution

ABSTRACT

Apparatus for performing a liquid-liquid extraction and electrolysis comprising a closed hollow container equipped with means for countercurrently contacting streams of liquid, means for creating turbulence in the liquid mixture, means for passing an electrical charge through the liquid mixture, and means for retarding the passage of liquid through the container. In one embodiment, the means for creating turbulence in the liquid mixture comprises a rotatable shaft with agitator blades mounted thereon and, in another embodiment, comprises a pulse wave generator. The apparatus is capable of carrying out a wide variety of liquid-liquid extractions and electrolysis reactions, but is particularly applicable to processes for changing the valence state of a metal of variable valence state to effect its separation from other metals and for concentrating metals of variable valence state in solution. In the process of the invention simultaneous valence change of a metal of variable valence state and concentration of that metal in aqueous solution is accomplished by passing a continuous stream of an aqueous solution through a column, passing a continuous stream of an organic solution of at least one metal of variable valence state which is preferentially soluble in the aqueous solution in its changed valence state countercurrently through the column, while maintaining the flow ratio of organic solution to aqueous solution greater than 1:1, forming a dispersion containing a continuous aqueous phase by creating turbulence in a zone where both the aqueous solution and the organic solution are present, allowing the dispersion to contact one electrode of an electrolytic cell which has its electrodes separated by a porous membrane, passing an electric current through the dispersion, and separating the immiscible organic and aqueous phases. This process is particularly useful to reduce hexavalent uranium to tetravalent uranium, to reduce tetravalent plutonium to trivalent plutonium, to concentrate these metals in solution in their changed valence states, and to separate plutonium from uranium.

llited States Patent [1 1 Gray et al.

1 Nov. 6, 1.973

[ APPARATUS FOR ELECTROLYTIC OXTDATION ORREDUCTION, CONCENTRATION, ANDSEPARATION OF ELEMENTS lN SOLUTllON [75] Inventors: John H. Gray; AlfredSchneider,

both of Morristown, N.J.; Anthony F. Cormak, Tonawanda, N.Y.; Arnold L.Ayers, Convent Station, NJ.

[73] Assignee: Allied Chemical Corporation, New

York, NY.

[22] Filed: Aug. 24, 1971) [21] Appl. No.: 66,310

Primary Examiner-John H. Mack Assistant ExaminerW. 1. SolomonAttorneyErnest A. Polin and Luther A. Marsh [57] ABSTRACT Apparatus forperforming a liquid-liquid extraction and electrolysis comprising aclosed hollow container equipped with means for countercurrentlycontacting streams of liquid, means for creating turbulence in theliquid mixture, means for passing an electrical charge through theliquid mixture, and means for retarding the passage of liquid throughthe container. In one embodiment, the means for creating turbulence inthe liquid mixture comprises a rotatable shaft with agitator bladesmounted thereon and, in another embodiment, comprises a pulse wavegenerator. The apparatus is capable of carrying out a wide variety ofliquid-liquid extractions and electrolysis reactions, but isparticularly applicable to processes for changing the valence state of ametal of variable valence state to effect its separation from othermetals and for concentrating metals of variable valence state insolution.

In the process of the invention simultaneous valence change of a metalof variable valence state and concentration of that metal in aqueoussolution is accomplished by passing a continuous stream of an aqueoussolution through a column, passing a continuous stream of an organicsolution of at least one metal of variable valence state which ispreferentially soluble in the aqueous solution in its changed valencestate countercurrently through the column, while maintaining the flowratio of organic solution to aqueous solution greater than 1:1, forminga dispersion containing a continuous aqueous phase by creatingturbulence in a zone where both the aqueous solution and the organicsolution are present, allowing the dispersion to contact one electrodeof an electrolytic cell which has its electrodes separated by a porousmembrane, passing an electric current through the dispersion, andseparating the immiscible organic and aqueous phases. This process isparticularly useful to reduce hexavalent uranium to tetravalent uranium,to reduce tetravalent plutonium to trivalent plutonium, to concentratethese metals in solution in their changed valence states, and toseparate plutonium from uranium.

22 Claims, 17 Drawing Figures Emma States Patent 1 11 3,77@,6l2 Gray etah.

[ Nov. 6, 1973 PATENTEBHUY 61973 SHEET 3 BF 6 INVENTORS.

HY DRAUHC.

PULSING DEV\CE BY K 7 ATTORNEY PATENTFnHnv ems 3.770.612 SHEET NF 6ATTOFLTEK APPARATUS FOR ELECTROLYTIC OXIDATION OR REDUCTION,CONQIENTRATION, AND SEPARATION OF ELEMENTS IN. SOLUTION CROSS-REFERENCESTO RELATED APPLICATIONS Co-pending application of Alfred Schneider andArnold L. Ayers, entitled Electrochemical Concentration of MetallicSolutions, Ser. No. 815,713, filed Apr. 14, 1969, now U.S. Pat. No.3,616,275.

Co-pending application of Alfred Schneider and Arnold L. Ayers, entitledElectrochemical Oxidation or Reduction, Ser. No. 815,714, filed Apr. 14,1969, now U.S. Pat. No. 3,616,276.

BACKGROUND OF THE INVENTION Various industrial separation processesrequire treat ment of metal compound containing solutions in which themetal, which is a metal of variable valence, is in a particular valencestate. For example, tetravalent uranium compounds, such as U1 can beprecipitated from organic solutions with HF. Since uranium is generallyin a higher valence state, particularly the hexavalent form, it must bereduced to the tetravalent state prior to the precipitation operation.

In another example in the nuclear fuels reprocessing art, mixtures oftetravalent plutonium and hexavalent uranium in organic solution can beseparated from each other by selective extraction with an immiscibleaqueous solution whereby the uranium remains in the organic phase andthe plutonium transfers to the aqueous phase. The plutonium, which isgenerally in its tetravalent state, must be reduced to the trivalentstate in order to permit this separation.

It is known that such changes in valence state can be effected by meansof a reducing agent such as iron. While such reducing agents effectivelyreduce the metal in the metal compound, contamination of the solutionwith the added metal results The contaminant metal must then be removed,thereby adding to the cost of the process.

It is also known that the addition of tetravalent uranium to mixtures ofhexavalent uranium and tetravalent plutonium organic solution reducesthe plutonium to its trivalent state. This method eliminates the needfor addition of a contaminant metal, but has the disadvantage that theadded uranium may change the isotopic composition of the hexavalenturanium product. Further, the addition of uranium also adds materiallyto the cost of such process.

U.S. Pat. No. 3,361,651 discloses that tetravalent plutonium in a dilutenitric acid solution with hexavalent uranium can be reduced to itstrivalent state electrolytically. This process has the disadvantage thatthe metals must be in aqueous solution. In order to obtain the metals inaqueous solution, they must first be extracted with a nitric acidsolution.

For various purposes, it is necessary to have available metal solutionssuch as those obtained by the separation methods described above, inparticular concentrations. Evaporation of the solvent is the usualmethod of concentrating dilute aqueous solutions of one or more metals.In the case of metals obtained from the reprocessing of nuclear fuels,and plutonium in particular, such method is disadvantageous becauseplutonium may be lost due to polymerization and subsequentprecipitation. The plutonium could be concentrated by forming aprecipitate, as with oxalic acid, and then dissolving the precipitate,however, the apparatus required for these steps is complex, therebyadding considerable cost to the process.

There is a need in the art for method and apparatus for changing thevalence state of a metal of variable valence state, such as uranium,plutonium and neptunium, to a desired valence state to accomplishspecific separations and for concentrating metal compounds to a desiredlevel. It would be particularly desirable to have available such methodand apparatus which are capable of effectuating valence state change andconcentration simultaneously, thereby saving operating time and avoidingthe need for separate, more bulky equipment.

SUMMARY OF THE INVENTION It is an object of the invention to provide anim proved apparatus for contacting two immiscible liquids underelectro-lytic conditions. It is another object of the invention toprovide an improved method and apparatus for changing the valence stateof a metal of variable valence state.

Another object of the invention is to provide a method and apparatus forsimultaneously changing the valence state of a metal of variable valencestate to effect the preferential transfer from one liquid phase to theother and concentrating the metal in changed valence state to a desiredlevel.

It is another object of the invention to provide such method andapparatus which is additionally capable of effectuating a separationbetween aqueous and organic phases.

It is still another object of the invention to provide an improvedmethod and apparatus for separating plutonium from uranium in organicsolution and concentrating the plutonium in the aqueous solution thusobtained.

Still another object of the invention is to provide an improved methodand apparatus for reducing hexavalent uranium to tetravalent uranium andconcentrating the tetravalent uranium to a desired level.

Another object of the invention is to provide an improved method andapparatus for reducing tetravalent plutonium to trivalent plutonium topermit reextraction from an organic into an aqueous phase and forconcentrating the trivalent plutonium to a desired level.

Other objects and advantages of the invention will become apparent fromthe following description.

In accordance with one aspect of our invention, we have designedapparatus which fulfills the above-stated objects. The apparatus maytake the form of the following described embodiments.

In one embodiment, there is provided a closed hollow container, a ventfor gases at the top of the container, an inlet and an outlet for liquidat one end of the container, an inlet and an outlet for liquid at theopposite end of the container, a first electrode member mounted withinthe container, a second electrode member mounted within the container, aporous membrane separating the two electrode members, thereby defining afirst electrode chamber and a second electrode chamber, a plurality ofbaffle plates mounted in spaced relation within the second electrodechamber which baffle plates may optionally be constructed of anelectrically conducting material and, in such :an event, may replace thesecond electrode, and means for creating turbulence in liquid charged tothe second electrode chamber.

Preferably, the container is a column having one dimension substantiallylonger than the other and includes a plurality of baffle plates inaddition to the first and second electrodes.

The turbulence in liquid charged to the second electrode member may becreated by any suitable means. In a specific embodiment of theinvention, it comprises a rotatable shaft extending longitudinallythrough the chamber, agitator blades mounted in spaced relation on theshaft and means for rotating the shaft. In another embodiment of theinvention, the turbulence is created by pulsing liquid either throughapertured plates mounted in spaced relation within the second electrodechamber or'through conventional packing material. If the secondelectrode member is equipped with packing material, the baffles in thatchamber may be omitted.

In a preferred embodiment, the apparatus is free of baffleplates and/oragitator blades in the vicinities of its endwalls so that separation ororganic and aqueous phases can take place in these areas.

A variety of liquid-liquid extractions under electrolytic conditions maybe carried out in the abovedescribed equipment. The equipment isparticularly useful, however, for processes for simultaneously changingthe valence state of a metal of variable valence state and concentratingmetals inchanged valence state in aqueous solution, and for separatingmetals of variable valence state by changing their valence state so thatone of them is preferentially soluble in an aqueous solution in which itbecomes concentrated. Such procedures constitute the process aspect ofour invention.

The process is carried out by passing a continuous stream of an aqueoussolution through a column, passing a continuous stream of an organicsolution of a metal of variable valence state which is preferentiallysoluble in the aqueous solution in its changed valence statecountercurrently through the column while maintaining the flow rateratio of organic solution to aqueous solution greater than 1:1, forminga dispersion containing a continuous aqueous phase by creatingturbulence in a zone where both the aqueous solution and the organicsolution are present, allowing the dispersion to contact one electrodeof an electrolytic cell which has its electrodes separated by a porousmembrane, passing an electric current through the dispersion, andseparating the immiscible organic and aqueous phases.

In a preferred embodiment there are maintained at the extremities of thecolumn relatively quiescent zones wherein separation of organic andaqueous phases occurs.

Oxidation or reduction may be effected by adjusting the polarity of theelectrodes which govern the passage of electricity through the system.Thus, when the electric current is passed through the dispersion whichis in The above-described apparatus and process are particularly adaptedfor application in the area of nuclear fuel reprocessing using a Purextype process. In such applications, reduction and effective separationof plutonium from uranium may be effected without contamination oruranium isotopic alteration, the plutonium may be reduced to a lowervalence state and stripped from the solution and the concentration ofplutonium in the aqueous product stream may be adjusted to desiredlevels.

As already noted, specific reduction procedures to which the apparatusand process of the invention are particularly suited are those involvingreduction of hexavalent uranium to tetravalent uranium and thoseinvolving reduction of tetravalent plutonium to trivalent plutonium. Anexample of an oxidation procedure used to separate elements would be theoxidation of a system containing tetravalent plutonium and tetravalentneptunium. Both these elements extract well into organic solution. Bothwould be oxidized, Pu into Pu and Np into Np (NpO but Np can be made totransfer preferentially into an aqueous phase.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view inpartial half section of an illustrative embodiment of the apparatus ofthe invention characterized by anode and cathode members which arehollow screens extending longitudinally within the container, and bypulsing means for creating turbulence.

FIG. 2 is a top view of a section of FIG. 1, taken along line 22 of FIG.1, which illustrates a top view of one of the baffle plates in thecolumn.

FIG. 3 is a top view of a section of FIG. 1, taken along line 33 of FIG.1, which shows a top view of one of the apertured plates.

FIG. 4 is an elevational view in partial half section of anotherembodiment of the apparatus of the invention which is similar to theembodiment shown in FIGS. 1-3, except that the cathode comprises aplurality of horizontally disposed screens within the cathode chamber.

FIG. 5 is a top view of a section of FIG. 4, taken along line 5-5 ofFIG. 4, showing the top view of one of the horizontally disposed screenswithin the cathode chamber.

FIG. 6 is a top view of a section of FIG. 4, taken along line 6-6 ofFIG. 4, showing a top view of one of the apertured plates.

FIG. 7 is an elevational view in partial half section of anotherembodiment of the invention which is similar to the embodiment of FIGS.1-3, except that the cathode screens are arranged in a diamond patternthroughout the length of the column.

FIG. 8 is a top view of a section of the apparatus embodiment of FIG. 7,taken along line 88 of FIG. 7, showing the top of one of the baffleplates in the column. 1

FIG. 9 is a top view of a section of the apparatus embodiment of FIG. 7,takenalong line 9-9 of FIG. 7, which shows a portion of a cathode screenand a portion of one of the apertured plates in the column.

FIG. 10 is an elevational view in partial half section of anotherembodiment of the invention, which apparatus contains concentricelectrode screens, a plurality of baffle plates, and means for creatingturbulence which comprises a rotatable shaft extending longitudinallythrough the chamber, agitator blades mounted on the shaft and means forrotating the shaft.

FIG. II is a top view of a section of FIG. Id, taken along line llll1llof FIG. I0, showing the orientation of the circular screens and thearrangement of several agitator blades on the rotatable shaft.

FIG. I2 is a top view of a section of the apparatus embodiment of FIG.10, taken along line ll2-ll2 of FIG. 10, showing a top view of one ofthe baffle plates.

FIG. 13 is an elevational view in partial half section of anotherembodiment in accordance with the invention which is provided withbaffle plates, an internal longitudinally disposed anode screen, acathode which constitutes a plurality of spaced horizontally disposedscreens, and pulsing means for creating turbulence.

FIG. M is a top view of a section of the apparatus embodiment of FIG.13, taken along line ]14-I4 of FIG. 13, showing the top of one of thehorizontally disposed screens and its relationship to the internal anodescreen.

FIG. 15 is a top view of a section of the apparatus embodiment of FIG.113, taken along line 15-15 of FIG. I3, which shows a top view of one ofthe apertured plates in the column and its relationship to the internalanode screen.

FIG. 16 is a partial elevation in partial half section of anotherembodiment of the invention in which the anode is an internallongitudinally disposed hollow screen member, the cathode constitutes aplurality of horizontally disposed screens, and in which the means forcreating turbulence in the second electrode chamber comprises packingthroughout the second electrode chamber and means for pulsing a liquidthrough the packing.

FIG. I7 is a top view of a section of FIG. 16, taken along line ]l7]l7of FIG. I6, showing a top view of a section of the packed secondelectrode chamber and a section of the internal anode chamber.

DETAILED DESCRIPTION OF THE INVENTION AND OF THE PREFERRED EMBODIMENTSThe materials of construction for the container body, the electrodes,the porous membrane, the apertured plates and the baffle plates, shouldbe inert or resistant to reaction with the materials charged to theapparatus and the products prepared therein. Depending on suchconsiderations, illustrative suitable materials of construction for thecontainer body, the apertured plates, and the baffle members, are steel,polytetrafluoroethylene, carbon and nickel, as appropriate. Theelectrodes may be constructed of electrically conductive materials suchas carbon, nickel, iron, tantalum, niobium and noble metals such as goldand platinum. When the apparatus is used for nuclear fuel reprocessing,in accordance with the preferred embodiment to be described in moredetail hereafter, the preferred materials of construction for theelectrodes are the noble metals, particularly gold or platinum. When thebaffle plates serve as an electrode, they are then, of course,constructed of an electrically conductive material as described above.

The porous membrane, which separates the electrodes and defines thefirst and second electrode chambers, may be constructed of any materialwhich will permit hydrogen ion diffusion and yet be impervious to largecation/migration such as migration of Pu and U0 In this way the porousmembrane prevents anolyte and catholyte mixing. Some porosity isdesirable in order to permit the passage of current at a low voltage.Use of low voltages in the apparatus and process of the invention ispreferred in order to minimize heat generation and reduce undesirableside reactions. The porous membrane should have a reasonable degree ofstructural strength and for this reason is preferably constructed of aceramic material. Sintered porous A1 0 has been found to be particularlyeffective for use in treatment of uranium and plutonium solutions. Theporosity is not absolutely critical. The optimum porosity will vary withthe specific materials treated. With plutonium and uranium solutions, ithas been found that sintered A1 0 having a porosity of about l1O micronsis especially effective. Depending on the materials treated andparticular needs, organic membranes may also be employed. Illustrativeare the ion exchange membranes which are generally available as ananionic or cationic exchange resin in a film forming matrix such aspolyethylene or a vinyl resin. Other suitable membrane materials willreadily occur to those skilled in the art.

The electrodes may be orientated and arranged in any convenient manner.Either the anode or cathode, or both, may be single integral members ora plurality of members. The only requirement is that a porous membranemust separate the electrodes into two elec trode chambers. Thus, theelectrodes may be in the form of solid hollow tubes extending into thecontainers. These tubes may be arranged concentric to one another orsituated alongside one another. For reasons of economy, particularlywhen the electrode members are constructed of noble metals, they areprovided in the form of screens, thereby providing large surface areas,but diminishing the quantity of noble metal material required. In apreferred embodiment, the surface area of one of the electrode members,preferably the cathode member, is increased by providing a plurality ofspaced screens. These screens may be disposed in any convenientconfiguration within its chamber, such as vertically, horizontally or ina diamond-type pattern, as shown in FIG. 7. Preferably, when a pluralityof screens are employed, they are disposed laterally in proximity topulse plates and/or baffle plates, as may be desired, and mostpreferably, are orientated perpendicular to the porous membrane.

Baffle plates are provided in order to afford a means of control overthe flowof liquids in the container. The plates are dimensioned andpositioned so as to provide a hold-up of liquids in the container andparticularly to provide liquid hold-up in the vicinity of the cathodemember. This is particularly important where the cathode constitutes aplurality of members. The number and arrangement of the baffles are notabsolutely critical and may be readily optimized by persons skilled inthe art, dependent on apparatus design and particular materials treated.In those embodiments where turbulence is created in liquid charged tothe second electrode chamber by pulsing means, the baffle plates mayserve as pulse plates by providing apertures in the baffle platesthrough which liquid is then pulsed. The number and arrangement of theapertures is not absolutely critical and may be readily optimized bypersons skilled in the art, taking into consideration the desiredbaffling effects, if any, desired to be achieved by the apertured pulseplates. Preferably, in order to achieve the combination of effectivepulsing and the hold-up in the desired areas of the container, acombination of apertured pulse plates and baffle plates are employed.The baffle plates, which as explained above, may serve as pulse plates,may also serve as the second electrode by merely constructing them outof a suitable electrically conductive material. In the preferredembodiment, however, a separate second electrode is provided, and baffleplates are additionally provided, with or without apertured pulseplates, depending on the turbulencecreating means employed.

In the broad aspects of the invention, any suitable means may beprovided to create turbulence in liquid charged to the second electrodechamber. Critical to the obtainment of particularly good results inaccordance with the preferred embodiments of the invention is theprovision of certain specific types of turbulencecreating means. Onesuch means is the provision of a rotatable shaft which extendslongitudinally through the second electrode chamber. Agitator blades aremounted in spaced relation on the rotatable shaft and means are providedfor rotating the shaft. Preferably, there should be provided a pluralityof agitator blades which are spaced evenly along the shaft. In a morepreferred embodiment, the shaft is free of agitator blades and thecontainer is free of baffle plates in the vicinities of the end walls ofthe container. This provides relatively quiescent zones at theextremities of the container and permits separation of lighter organicand heavier aqueous phase in those regions.

In another embodiment, pulsing means are provided for creatingturbulence in liquid charged to the second electrode chamber. This maycomprise a plurality of apertured plates mounted in spaced relationwithin the second electrode chamber or conventional packing materialwithin and means for pulsing liquid through the apertured plates andthrough the packing material. If a packing material is employed, it mayconstitute any of the conventional materials used in the art to packcolumns such as distillation columns. Illustrative suitable packingmaterial includes Raschig rings, glass beads and the like. The purposeis to provide a packed inert material with a large surface area. Anysuitable means for creating the pulse waves may be employed. The pulsewaves may be created, for example, by a hydraulic pulsing device locatedoutside the container. This hydraulic pulsing device can pulse one ofthe liquids desired to be charged into the container through theapertured plates, preferably. upwardly. The pulsed liquid may besupplied through the main feed source for the liquid, but preferably isprovided through a separate leg. This is to permit a continuous supplyof unpulsed liquid to be fed into the container. In a still preferredembodiment, the container is free of pulse plates and baffle plates inthe vicinity of the end walls thereof to provide relatively quiescentzones in those areas to permit settling of the heavier'aqueous phase.

Preferably, the apparatus is provided with means for cooling at leastone of the electrode chambers. This may comprise a liquid which iscirculated within such electrode chamber, such as water or a dilute acidsolution, such as dilute I-INO or a cooling coil which is inserted intothe chamber as is shown, for example, in FIG. 13. Obviously, if one ormore of the electrode chambers is to be cooled by circulation of aliquid, suitable accesses to and from the chambers and circulating meansmust be provided. In such an event, it is also desirable to providecooling means for the recirculating liquid and a vent for releasinggases which may collect in the chamber.

The apparatus in the invention may be used for performing a variety ofliquid-liquid extraction and electrolysis operations. In accordance withthe preferred embodiment of the invention, the apparatus is particularlyuseful in processes in which it is desired to simultaneously change thevalence state of a metal of variable valence state to effect itstransfer to the aqueous phase and concentrate the metal of changedvalence state in an aqueous solution. Co-pending U. S. applications Ser.Nos. 815,713 and 815,714, mentioned supra, claim procedures wherebythese procedures are carried out in single stages. The present process,in one aspect, provides an improvement in these procedures, wherebyvalence state change, preferential ion transfer from one phase toanother and concentration can be simultaneously effected within the samemulti-stage apparatus. The process of the invention also provides ameans for improving the efficiency of these separate procedures. In apreferred embodiment of the invention, separation of aqueous and organicphases may be effected simultaneously with the oxidation or reductionand concentration and in the same apparatus.

From a procedural standpoint, the valence of one or more metals ofvariable valence state in an organic solution is changedelectrochemically by forming a dispersion between the organic solutionand an immiscible aqueous solution and passing an electric currentthrough the dispersion. The streams of aqueous solution and organicsolution are preferably passed countercurrently in contact with eachother. The dispersion is created so that a continuous aqueous phase ismaintained in the system. The presence of a continuous aqueous phase maybe monitored by observing the level of the interface between the aqueousand organic phases, by observing the weight of liquid in the column andby observing voltages maintained in the column. A drop in any of theseconditions may indicate a shift towards a continuous organic phase. Thismust be avoided and the continuous aqueous phase may be maintained byadjusting the flow rates of organic and aqueous solutions so that agreater volume of aqueous solution is charged to the column, byregulating the intensity and amount of turbulence created in thedispersion or by suitable design of the baffles. If reduction (a lowervalence state) is desired, the dispersion is allowed to contact thecathode of the electrolytic cell. If oxidation (a higher valence state)is desired, the dispersion is allowed to contact the anode of theelectrolytic cell. The anode and cathode members may be interchanged bymerely changing vthe polarity of the terminals of these members so thatthe electric current passes first into one rather than the other.Concentration of the metal in changed valence state in one of thephases, particularly the aqueous phase, may be accomplished by passing acontinuous stream of an organic solution of the metal of variablevalence state which is preferentially soluble in aqueous solution in itschanged valence state through the column such that the flowrate ratio oforganic solution to aqueous solution is always greater than one.Provided that a continuous aqueous phase is maintained in the system,under these conditions there will result a simultaneous valence changeof metal and concentration of the metal in the aqueous phase' Theconcentration factor will vary depending on the metals treated and theflow-rate ratios of organic solution to aqueous solution. This may bedetermined by routine experimentation. In the case of reduction oftetravalent plutonium to trivalent plutonium, the concentration factoris in direct proportion to the flow rate ratio of organic solution toaqueous solution. For example, if the flow rate ratio of organic toaqueous solution is 2:1, the plutonium will be concentrated in theaqueous solution by a factor of 2, i.e. it will be twice as concentratedin aqueous solution as originally charged in organic solution.

Any inert solvent which will dissolve the metal compound in the valencestates desired may be employed. Organic solvents are convenient but maynot dissolve heavy metal compounds such as those of uranium andplutonium. Such compounds, however, are known to form complexes whichare soluble in organic solvents. Any complexing agent yielding a metalcomplex soluble in an organic solvent may be employed. Suitablecomplexing agents include the alkyl phosphates, aliphatic ketones suchas hexone and aliphatic amines such as dioctylamine. The alkylphosphates can be mono, dior tri-esters of phosphoric acid derived fromalkanols containing one to about eight carbon atoms such as butanol,hexanol, octanol and the like. Any inert organic solvent may beemployed. The preferred solvents are hydrocarbons such as dodecane,kerosene, gasoline and the like. Tributyl phosphate in an amount of fromto 40 percent by weight in a hydrocarbon is preferably employed assolvent for metals formed in nuclear fuels, i.e. uranium, plutonium andneptunium, due to its high extraction selectivity. The proportion oforganic solvent to complexing agent is not critical. Generally, enoughof the organic solvent should be present to maintain a dispersion of theaqueous and organic solutions and prevent an emulsion from forming.Normally, at least about 5 percent by weight of the organic solvent inthe complexing agent-solvent mixture will accomplish this purpose. Theproportion of complexing agent in the mixture is preferably from 5-95percent by weight of the mixture.

The aqueous solution must be immiscible with the organic solution andmust be an electrolyte. Suitable aqueous solutions are dilute mineralacid or salt solutions, such as nitric acid, sodium nitrate and thelike. In a reduction procedure, the aqueous solution may contain astabilizer, such as hydrazine, to prevent reoxidation of the metals. Apreferred concentration of hydrazine, if employed, is from ababout 0.01to about 0.5M. In an oxidation procedure, an anti-reductant, such as HNOor HaNO could be added to the system.

When the concentration of the metal in the organic solution to beoxidized or reduced is quite low, the rate of the oxidation or reductiondecreases and longer reaction times are required to complete thereaction. In order to increase the rate of reaction an internalreduction oxidation (redox) agent can be added to the system. Such redoxagent is reduced or oxidized by the passage of a current through thecell. When the metal whose valence state is to be changed is to bereduced, the redox agent is reduced, in turn reduces the metal whosevalence is to be reduced, and is itself oxidized back to its originalvalence state. The concentration of this agent will remain substantiallyconstant. The addition of an internal redox agent is particularlyeffective when added to dilute solutions of tetravalent plutonium. Asmall amount of uranyl nitrate [UO (NO is generally added to the organicsolution as the redox agent. During the reaction, the hexavalent uraniumis reduced to tetravalent uranium, which reduces the tetravalentplutonium, and is then reoxidized to hexavalent uranium according to theequation:

2 PU n 2 PU 11+ The rate of this reaction is rapid and increases therate of reduction of plutonium. The choice of uranium is particularlyconvenient in this instance since the hexavalent uranium and anytetravalent uranium will remain in the organic phase while most of thetrivalent plutonium will transfer to the aqueous phase. Thus, theaddition of the redox agent in this case will not contaminate thetrivalent plutonium solution. This process is particularly useful foreffecting the transfer of plutonium from an organic to an aqueoussolution as is required for the purification processes employing solventextraction, e.g., the Purex type process.

The electrochemical conversions may be carried out over a wide range oftemperature and pressure conditions. The only limitations are thefreezing point and the vapor pressure of the electrolyte. Means forheating, cooling or maintaining desired pressure conditions couldaccordingly also be provided.

The amount of electric current which is passed through the cell is notabsolutely critical. The optimum rate is that which is high enough togive a satisfactory reaction rate but low enough so that an undesirabledegree of corrosion or disintegration of the electrodes will not takeplace. The optimum amperage and voltage values to employ depend on theabove factors and also on such factors as the configuration of theparticular cell involved, the reaction rates desired and the partic ularmaterials treated. The determination of these optimum values and themaintenance of same in the electrolytic cell are within the skill ofthose persons skilled in the art of conducting electrolytic procedures.

'The invention will now be fully described with'particular reference tothe embodiments shown in the draw ings.

Referring to FIG. 1, the closed. hollow container 10 serving as theelectrolytic cell is preferably a column having one dimensionsubstantially longer than the other which column is additionallycharacterized by having a wider diameter at the bottom than at the top.The smaller diameter side wall is shown as 15. The larger diameter sidewall is shown as 19. Flange 20 connects walls 15 and 19, It is to beunderstood that when the term closed is employed, this is notnecessarily intended to mean permanently closed. Thus, the column couldbe closed with removable closure members which, when in the closedposition, will provide a gastight housing. Top end wall 11 of the cellis provided with a vent 12 for releasing hydrogen and other gases andalso with an inlet 13 for admitting liquid to the top of the cell. Anoutlet 14 for removing liquid from the cell is located in the side wall15 of the cell in proximity to the top of the cell. Support column 16extends along the longitudinal axis of cell column 10 from bottom endwall 17 through top end wall 11. A porous ceramic membrane 18 which isin the shape of a hollow cylinder extends from flange 20 downwardly tobottom wall 17. Cell 10 is also provided with liquid inlet 21, liquidoutlet 22 and pulsing leg 23 having access to the cell through bottomwall 17. Hydraulic pulsing device 24 is connected to pulsing leg 23.Cylindrical anode screen 25 is positioned between porous membrane 18 andcell wall 19 along a portion of the length of the column. Anode leadwire 26 connects anode screen 25 with an electric circuit and passesthrough cell wall 19 through insulator 27. The porous membrane 18, cellside wall 19, flange 20 and cell bottom wall 17 define anode chamber 45which contains an anolyte solution which cools anode screen 25. Vent 52is provided for the release of volatile gases from chamber 45. Pump 53and return pipe 54 recirculate the anolyte solution. Cooling coil 50 islocated on return pipe 54 to cool the recirculating liquid. The internalarea defined by porous membrane l8 defines a cathode chamber 46. Cathodescreen member 28 is suspended within cathode chamber 46 by means ofsupporting brackets 29 and 31. Cathode lead wire 33 connects cathodescreen 28 to an electric circuit and passes through top wall 11 of cellthrough insulator 34. Baffle plates 35, 36, 37, 38 and 39 are mounted onsupporting column 16 in spaced relationship to one another. A top viewof baffle 36 and its relationship to anode screen 25 and cathode screen28 is shown in FIG. 2. Apertured plate members 40, 41,

42, 43 and 44 are mounted on supporting column 16 in alternatingrelationship with baffle plates 35-39. The apertured plates haveregularly arranged apertures around the circumference thereof, but arenot perforated in the center. The arrangement of the apertures is shownby the top view of aperture plate 42 in FIG. 3. Supporting column 16does not have any apertured plates or baffle plates at its uppermost endor lowermost ends'thereby leaving disengaging zones or quiescent zonesin which no turbulence is created and in which settling of the heavieraqueous phase can take place. Separation of the immiscible organic andaqueous phase takes place in the top disengaging zone which is definedby the distance from uppermost baffle plate 35 to outlet 14. The bottomdisengaging zone is defined by the distance between the lowermostapertured plate 44 and the bottom wall 17. A pool of aqueous liquid willcollect in this zone.

In the operation of the cell illustrated in FIGS. 1-3, a measured volumeof a metal of variable valence state in organic solution is charged tocathode chamber 46 which contains an equal volume of an aqueouscatholyte solution. Anode chamber 45 is filled with a suitable anolytesolution. Additional aqueous solution and additional organic solutionare continuously fed into cathode chamber 46 through inlets 13 and 21,respectively.

At the same time, both solutions are pulsed in the cathode chamber 46through pulse leg 23 upwardly through apertured pulse plates 40, 41, 42,43 and 44. The flow rate of thetotal volume of organic solution fed tocathode chamber 46 is adjusted as desired in relation to the rate atwhichthe aqueous catholyte solution is fed to the chamber. The organicand aqueous solutions contact each other in cathode chamber 46 and forma dispersion characterized by the presence of a continuous aqueousphase. At the same time, an electric current is passed through thedispersion in the cathode chamber 46 of the cell. Reduction of reduciblemetal of variable valence state takes place and any metal of lowervalence state which is preferentially soluble in aqueous solution passesinto the aqueous phase. Separation of aqueous and organic phases takesplace in the top disengaging or quiescent zone of the column wherein theinterface is designated by 47, the heavier aqueouscontinuous dispersionis shown by 48 and the lighter organic phase is shown by 49. A pool ofaqueous liquid collects in the bottom disengaging zone which is shown by51. Aqueous solution is withdrawn from the system through outlet 22;organic solution is withdrawn from the system through outlet 14.

In the description of the remaining Figures, in order to facilitatedescription by comparison with the embodiment of FIGS. 1-3, similarcomponents will be shown with the same numerals.

FIGS. 4, 5, and 6 illustrate another embodiment of the invention whichis identical to that shown by FIGS. 1-3 with the following differences:In this embodiment, cathode screen 28, in lieu of being a verticalhollow tube as shown in FIGS. l-3, constitutes a plurality of laterallydisposed screens which are disposed perpendicular to the porous membraneand which alternate with the pulse plates. The embodiment of FIGS. 4-6has no separate baffle members. The apertured plates are perforated onlyover a small portion of their surface and the unperforated portionsserve as the baffling means. Another difference is that the cathode leadwire 33, instead of being a separate component as shown in FIG. 1, isnow the supporting column 16 which is in contact with all the cathodescreen members 28. In FIG. 4, this is shown by the designation 16, 33.

The embodiment of FIGS. 7-9 is similar to the embodiment of FIGS. 4-6with the following differences. The electrode screen members 28 arearranged in a diamond type configuration throughout the length of thecolumn. The polarity of the electrodes in this embodiment is reversed sothat screen members 28 are now the anode and screen member 25 is now thecathode. Lead wire 33 conducts electricity from screen members 28. Inthis embodiment baffles are provided in addition to pulse plates. As inFIG. 1, the baffles are shown by the numerals 35-39 and the pulse platesare shown by numerals 40-44.

The embodiment of FIGS. 10-12 is similar to that of FIGS. 13, exceptthat in this embodiment agitator blades are used to create turbulence inthe cell instead of pulse waves. 16 is a rotatable shaft. Agitatorblades 55, 56, 57 and 58 are mounted in spaced relationship on rotatableshaft 16. Horizontal baffles 35, 36, 37, 38 and 39 in the form of discsare mounted on shaft 16 in alternating relationship with agitator blades55, 56, 57 and 58. Vertical baffle members 59, 60, 61 and 62, as bestseen in FIG. 12, support cathode screen 28 and annular baffle members63, 64, 65, 66 and 67. In this embodiment, pulse leg 23 and pulsingdevice 24 are omitted. In FIG. 11, for reasons of clarity, horizontalbaffle 37 is not shown.

The embodiment of FIGS. 13-15 is similar to the embodiment of FIGS. 4-6,with the following differences. Anode chamber 45 and anode screen 25 areinternal of cathode chamber 46. Cooling coil 68 is shown within theanode chamber. Perforated plates 40 and 44 are shown as the end platesof a spaced group of eight plates, six of which are not numbered. Vent52 is in side wall 79. The vent is partially blocked by annular baffleare shown for monitoring temperature in different portions of the unit.Depending on the readings obtained, the temperature in the monitoredspaces may be regulated by any conventional means such as cooling coil68 in anode chamber 45. Supporting legs 76 and 77 are shown in FIG. 13.Support rods 78, 79, 82 and 83 and supporting bracket 80 support thesuspension of porous membrane 18 within the cell.

The embodiment of FIGS. 16 and 17 is similar to the embodiment of FIGS.13-15. Only that portion of the cell between aqueous inlet 13 andorganic inlet 21 is shown. Instead of the spaced apertured plates, thecolumn is packed with Raschig rings shown by the numetal 81, which areretained by cathode screen members 28. (Both members are shown by thenumeral 28 in FIG. l6).

15 for these parts.

The following illustrate typical specifications and conditions forillustrative electrolytic reduction or oxidation procedures inaccordance with the invention. The data are presented in tabular form.Each example, as indicated, corresponds to a process carried out in oneof the embodiments shown by FIGS. 1, 7, 10 or 13. Unless otherwisespecified, the material of construction is stainless steel. In all theexamples, the internal diameters of organic inlet 21, organic outlet 14,pulse leg 23 (where applicable), aqueous outlet 22 and aqueous inlet 13,are 1 inch. The supporting or rotating column 16 has an internaldiameter of one-half inch. The numbers in the first column of the tablewhich are indicated parenthetically are the numerals used on thedrawings FIG. 1 FIG. 7 FIG. 7 FIG. 10 FIG. 13

Apertured plates (40-44) Diameter4%" Diameter4%".. Diameter-4%"...Diflmelcr" Free area-20%.. Free areal5 Free area-15% Free area- 15%.

Bafile plates (35-39).. Diameter-4%" Diameter-4%" Diameter-4%"Diameter-4%" Free area- 15% Free area- 10% Free area2()%..... Freearea-25%....

Cathode .l Platinum or gold..... Platinum or gold... Platinum or goldPlatinum or gold. Platinum or gold.

Cylindrical screen Cylindrical screen. Cylindrical screen Cylindricalscreen. Disc screens. Mesh size-28 Mesh size-20... Mesh size-20 Meshsize- 16 Cylinder diameter 5%"... Cylinder diamete Cylinder diameter 5 aCylinder diameter4/s.... Diameter l9 /n". Length2()".. Length-20Length20" Length-20" Anode Platinum cylindrical Platinum funnel Platinumfunnel Platinum cylindrical Platinum cylindrical screen. screen. screen.screen. screen. Mesh size-20 Mesh sizel6 Mesh size- 16 Mesh size-20 Meshsize-20. Cylinder diameter 5%... (ylinder diameter max. Cylinderdiameter rn Cylinder diameter Cylinder diameter 4%".

4%". min. l". 4 /2", min. I. l.ength20" Length-20" Length-20" Length-20"Lengthl6".

Cathode lead wire Platinum or gold Platinum or gold... Platinum orgold... Platinum or gold Platinum or gold.

Diameter /4" Diameter- A" Diameter- A Diameter- A1" Diameter- A".

Anode lead wire Platinum Platinum Platinum Platinum... Platinum.

Diameter-W Diameter-V4 Diameter- A! Diameter Diameter A.

Porous membrane (18) Sintered A120: lcnglh- Sintered A1 0 length-Cationic ion exchange Sintered AIQO lengtlh- Sintered AI OK: length-32"; l.D.-5"; wall 32"; I.D.5"; wall resin. 32": I,D.-5"; wall 32";l.D.5"; wall thickness A"; pore diameter-- l-ll) diameter- 1-10 microns.microns.

Disengaging (quiescent) zones Height 20' Height-20"..

I.D.5"..... I.D.5".

Aperatured plate spacing. inches. 3

Battle plate spacinginches 3 3 Cathode zonctheightininches)... 20 20Apertured plate zone (height in inches).

Baffle plate zone (height in inches).

Anolyte 2M HNO 2M HNO;,

(-atholyte 3M HNO;.. and 30 vol. 3M HNOn, and 30 vol.

percent tribtltyl phosphate in N dodecane.

percent tn'butyl ph thickness- W: pore phate in N-dodecane.

thickness- A"; po e diameterl-lO thickness W; pore diameterl-li)microns. microns.

Height-20" Height-2U". l.D.-5" I.D.-5".

2M HNO 2M HNQ, 2M HNO-i.

3M HNOII, and 30 vol. percenttributyl phosphate in N-dodecane.

3M HNOa, and 30 vol. percent tributyl phosphate in N-dodecane.

3M HNO;,. and 31) vol.

percent tributyl phosphate in N-dodecane.

Metal and initial valence state... U (U(),) (uranyl Np (neptunium ni- PuNp Pu U "(UO. (uranyl nitrate). Irate). nitrate). Pu" (plutoniumnitrate).

Aqueous flow rate (liters/minute). l l l l l()rganictlowrate(litcrs/minute)... 2 4 4 3 8 Aqueous to organic volumein l() 5 electrolytic zone.

Pulse frequency (cycles) Agitatorspeed 350 rpm... )0.

Pulse amplitude (inches) -34; -Vn A; /1.

Voltage................................. 4.5... 4.5 4.5 4.5 7.

(urreni density (ampslcntflnnln. (L05 (H15 0.05 0.05 0.05.

FIG 1 FIG. 7 FIG. 7 FIG. Fl(1.l3

Time ot'uperution thrs.) 2 3 3 3 3 Final valence state of metal.".......U Np *(NpOw Pu Np*"'(NpOz*) Pu Pu U (Pu trans- (Np transfers prefer ferspreferentially to entially to aqueous aqueous phase). phase).

Concentration factor 2 for Np 8 8 for Pu All mesh sizes are ofthe U.S.standard screen.

The top disengaging zone is the distance between the uppermost baffleplate, aperture plate, or top of the packed zone and the level definedby organic outlet 14. The bottom disengaging zone is the distancebetween the lowermost baffle plate or apertured plate on the bottom ofthe packed zone and the bottom We claim:

1. Apparatus for performing liquid-liquid extraction and electrolysiswhich comprises:

a. A closed packed hollow column,

b. a vent for gases at the top of the column,

0. an inlet and an outlet for liquid at one end of the column,

d. an inlet and an outlet for liquid at the opposite end of the column,

e. a first electrode member mounted within the container,

f. a second electrode member mounted within the container,

g. a porous membrane separating the two electrode members, therebydefining h. a first electrode chamber and i. a second electrode chamber,7

j. means for pulsing liquid through the column.

2. Apparatus according to claim 1 in which the means for pulsing liquidthrough the column includes packing material.

3. Apparatus according to claim 1 in which the means for pulsing liquidthrough the column includes a plurality of apertured plates.

4. Apparatus for performing liquid-liquid extraction and electrolysiswhich comprises:

a. A closed hollow container,

b. a vent for gases at the top of the container,

c. an inlet and an outlet for liquid at one end of the container,

d. an inlet and an outlet for liquid at the opposite end of thecontainer,

e. a first electrode member mounted within the container,

f. a second electrode member mounted within the container,

g. a porous membrane separating the two electrode members, therebydefining h. a first electrode chamber and i. a second electrode chamber,

j. a plurality of baffle plates mounted in spaced relation within thesecond electrode chamber which baffle plates may optionally beconstructed of an electrically conducting material and, in such anevent, may-replace the second electrode,.

k. a plurality of apertured plates mounted in spaced relation within thesecond electrode chamber, and

1. means for pulsing liquid through the apertures.

5. Apparatus according to claim 4 which includes a wall 17 of the cell.These disengaging zones are equal in height.

The use of uranium, plutonium or neptunium for each of the figurespresented was for illustrative purposes. Any or any combination of theseelements may be used in all ofthe figures.

Approximates.

plurality of baffle plates as described therein in addition to the firstand second electrodes.

6. Apparatus according to claim 5 in which one or more of the baffleplates are disposed substantially horizontally in the container.

7. Apparatus according to claim 6 in which the closed container is acolumn having one dimension sub stantially longer than the other.

8. Apparatus according to claim 4 in which the column is free ofapertured plates in the vicinities of the end walls of the column.

9. Apparatus according to claim 8 in which the electrode members arescreens of electrically conductive metals.

10. Apparatus according to claim 9 in which the electrode screens areconstructed of noble metals.

11. Apparatus according to claim 9 in which the porous membrane is aporous ceramic membrane.

12. Apparatus according to claim 11 in which the porous ceramic membraneis sintered A1 0 13. Apparatus according to claim 11 in which one of theelectrode members constitutes a plurality of spaced screens.

14. Apparatus according to claim 11 in which the electrodes are screensof noble metals, one electrode constitutes a plurality of spacedscreens, and in which the porous membrane is constructed of sintered M 015. Apparatus according to claim 8 in which:

a. the first electrode is in the form of a hollow tube extending withinthe column, and

b. the porous membrane is in the form of a hollow tube extending withinthe column and surrounding the first electrode.

16. Apparatus according to claim 15 in which the first electrode is inthe form of a screen.

17. Apparatus according to claim 16 in which the second electrodeconstitutes a plurality of spaced screens.

18. Apparatus according to claim 17 in. which each of the spaced screensis orientated perpendicular to the porous membrane.

19. Apparatus according to claim 18 in which the electrode screens areconstructed of noble metals.

20. Apparatus according to claim 19 in which the porous membrane isconstructed of sintered M 0 21. Apparatus according to claim 20 in whichthe first electrode chamber is provided with cooling means.

22. Apparatus according to claim 21 in which the noble metals areselected from gold and platinum.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,770,612 Dated November 6, 1973 Inventor(s) John Gray, AlfredSchneider, Anthony F. Cermak and Arnold L. Ayers It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Cover Page under heading [75] Inventors, "Cormak" should be I CermakCover Page under heading [57] Abstract, line 1 'performing a liquid"should read performing liquid Col. 2, line 20, "electro-lytic" should belectrolytic Col. 3, line 18, "member" should be chamber -5 Col. 9, line48, "ababout" should be about 001. 9, line 50, "MaNO should be H 0 Col.15, line 16, "A closed packed hollow" should read A closed hollow Signedand sealed this 7th day of May 197 4.

(SEAL) Attest:

.EDl-IARD l-Z.FLETCZ:E3Z,,,JR. ,C. MARSHALL DANN Attesting OfficerCommissioner of Patents FORM Po-1oso (ac-s9) USCOMM-DC 603764 69 UNITEDSTATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,770,612Dated November 6, 1973 Inventor(s) John Gray, Alfred Schneider, AnthonyF. Cermak and ArnoldL. Ayers It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

CoverPageunder heading [75] Inventors, "Cormak" should be Cermak CoverPage under heading [57] Abstract, line 1 "performing a liquid" shouldread performing liquid Col. 2, linei20, "electro-lycic" should beelectrolytic Col. 3, line 18, "member" should be chamber Col. 9, line48, "ababout" should be a.bO ut Col. 9 line 50, "NzaNO2" should be H 0Col. 15, line 16, "A closed packed hollow" should read A closed hollowSigned and sealed this 7th day of Play 197 4.

(SEAL) Attest: I

EDI-IAFID ILFLJBTCZIEEQJR. C. MARSHALL DANNY m- Attesting OfficerCommissioner of Patents FORM PO-IOSO (l0-69) USCOMM-DC B037 B-PGD

2. Apparatus according to claim 1 in which the means for pulsing liquidthrough the column includes packing material.
 3. Apparatus according toclaim 1 in which the means for pulsing liquid through the columnincludes a plurality of apertured plates.
 4. Apparatus for performingliquid-liquid extraction and electrolysis which comprises: a. A closedhollow container, b. a vent for gases at the top of the container, c. aninlet and an outlet for liquid at one end of the container, d. an inletand an outlet for liquid at the opposite end of the container, e. afirst electrode member mounted within the container, f. a secondelectrode member mounted within the container, g. a porous membraneseparating the two electrode members, thereby defining h. a firstelectrode chamber and i. a second electrode chamber, j. a plurality ofbaffle plates mounted in spaced relation within the second electrodechamber which baffle plates may optionally be constructed of anelectrically conducting material and, in such an event, may replace thesecond electrode, k. a plurality of apertured plates mounted in spacedrelation within the second electrode chamber, and l. means for pulsinglIquid through the apertures.
 5. Apparatus according to claim 4 whichincludes a plurality of baffle plates as described therein in additionto the first and second electrodes.
 6. Apparatus according to claim 5 inwhich one or more of the baffle plates are disposed substantiallyhorizontally in the container.
 7. Apparatus according to claim 6 inwhich the closed container is a column having one dimensionsubstantially longer than the other.
 8. Apparatus according to claim 4in which the column is free of apertured plates in the vicinities of theend walls of the column.
 9. Apparatus according to claim 8 in which theelectrode members are screens of electrically conductive metals. 10.Apparatus according to claim 9 in which the electrode screens areconstructed of noble metals.
 11. Apparatus according to claim 9 in whichthe porous membrane is a porous ceramic membrane.
 12. Apparatusaccording to claim 11 in which the porous ceramic membrane is sinteredAl2O3.
 13. Apparatus according to claim 11 in which one of the electrodemembers constitutes a plurality of spaced screens.
 14. Apparatusaccording to claim 11 in which the electrodes are screens of noblemetals, one electrode constitutes a plurality of spaced screens, and inwhich the porous membrane is constructed of sintered Al2O3. 15.Apparatus according to claim 8 in which: a. the first electrode is inthe form of a hollow tube extending within the column, and b. the porousmembrane is in the form of a hollow tube extending within the column andsurrounding the first electrode.
 16. Apparatus according to claim 15 inwhich the first electrode is in the form of a screen.
 17. Apparatusaccording to claim 16 in which the second electrode constitutes aplurality of spaced screens.
 18. Apparatus according to claim 17 inwhich each of the spaced screens is orientated perpendicular to theporous membrane.
 19. Apparatus according to claim 18 in which theelectrode screens are constructed of noble metals.
 20. Apparatusaccording to claim 19 in which the porous membrane is constructed ofsintered Al2O3.
 21. Apparatus according to claim 20 in which the firstelectrode chamber is provided with cooling means.
 22. Apparatusaccording to claim 21 in which the noble metals are selected from goldand platinum.